Flippers for swimming are generally provided with a large propulsion portion due to the presence of a flexible blade (flipper). Swimming flippers have, in addition to the flexible blade, a seating in the form of a shoe integral with the blade itself and enabling insertion of the foot of person wearing the flipper, for example the swimmer or underwater swimmer. The shoe in particular comprises a rear part which does not contain the foot, therefore open at the heel, for introducing the foot in the housing thereof.
Normally, for retaining the foot in the opening, this type of flipper has a strap or elastic belt hooked laterally of the flipper shoe.
In order to fit the flippers and fasten them to the underwater swimmer's foot, using elastic straps or other known fastening means, the underwater swimmer has to count on the assistance of another person or has to crouch with movements that are laborious and involve bending. These movements are conditioned, for most users, by their own weight and the weight of the equipment being carried, as the user has to stand on a single leg for the time needed to put on each flipper, and this generates significant difficulty.
This difficulty brings with it a high risk of falling and therefore of accidents, in particular when done not in conditions of leisure on a beach, but on rocks potentially wetted by the waves or on a slippery surface, for example due to the presence of seaweed, limpets and barnacles and so on. It is still more difficult to don the flippers on an unstable navigation means, such as, for example, a dinghy or a small or medium-size boat when rocking on a slightly rough or choppy sea and when there is a supporting surface that is slippery.
There is therefore a need to make flippers with special connections for the straps so that they are easily adjustable, as described in patents U.S. Pat. No. 4,795,384 and EP0687484. These systems are integrated with the flippers and, though more comfortable compared with conventional systems, they do not obviate demanding movements and hence the user having to bend, made necessary so as to reach the foot with the hands.
A further prior art disclosure is described in patent application WO9912612. It describes a flipper in which the normal strap is substituted with an apparatus having two static positions.
The first static position is lowered and leaves the opening of the shoe of the flipper free, keeping a strap of the connection between the shoe and the apparatus tautened, and the second static position is raised for keeping the foot inside the shoe.
The first stable position is realised by placing the fulcrum of rotation of the apparatus in a defined position of the shoe where the strap applies neither force nor momentum at any time about the anchoring pin, the lever arm being reduced substantially to zero, and therefore even if the strap is kept in tension, the apparatus remains in equilibrium in the first position.
A drawback of a solution of this type is that during use in underwater diving or swimming, the apparatus might pass from the second retaining position of the foot to the first position in an undesired and uncontrolled way, causing the loss of the entire flipper, as the strap is not always tensioned towards the second position. In particular, as the apparatus loosens, the momentum reduces progressively up to zero, reaching zero when it is in the first position. A further disadvantage is that the apparatus might pass beyond the pin anchoring element and therefore become positioned beneath the flipper in a position opposite the first position, making correct repositioning thereof extremely difficult, which could occur only with the person making very problematic bending movements, with the risks as set out above.
A further example of prior art is described in French patent application FR2744639. This patent describes a flipper which has a shoe, joined to the flipper, and a separate heel. The heel has a tongue, projecting forwards, which engages in an opening beneath the flipper. The position of the heel is adjustable as a function of the length of the user's foot. The tongue has a slot which has saw-tooth elements along an edge thereof. An opening clip, with a hook on a free end thereof, engages with the teeth to keep the tongue in position. The tongue is released by pressing on a pin which protrudes from the opening.
A disadvantage of this technique is that it is necessary for the user to act with the hands, in precarious equilibrium, for inserting the tongue in the clip, and this action has features of great uncertainty, difficulty and high instability, being extremely risky for the reasons set out in the foregoing.
A disadvantage shared by the entire prior art described above is that the flippers must be made with the provided devices and therefore these apparatuses are not applicable to traditional flippers already present on the market, or already in the possession of underwater swimmers.